Remove symmetrical sections from model
You could add a cube, use an array modifier on it (set it to 4), then on your plane use a boolean modifier set on Difference and target your cube. It could help to add a subdivision modifier set on simple on your plane too (prior to adding the boolean), in order to get enough geometry for the boolean modifier to work. You could also just have a mirror modifier on your plane and cut it manually, there is a ton of ways to do this :).